Wind turbine generators (e.g. self-excited or with permanent magnets) may be exposed to deformations of their rotor and/or stator due to the effect of operational loads (e.g. weight of the rotor/stator, electromagnetic forces between the rotor and stator, etc.). These deformations may cause degradation of the air gap between the rotor and the stator, said degradation producing bad performance and reduction of the life of the generator.
It is known, for example, that deformations of the rotor/stator and the consequent degradation of the air gap causes unbalanced attracting loads that generate a pull force. This pull force, which increases as air gap degradation increases, may affect the generator's performance, the life of the generator's components such as rotor, stator, generator bearing, elastic coupling and others components of the wind turbine (e.g. frames).
Nowadays, some designs put into practice generators with heavy parts for increasing the stiffness of the generator's components and, thus, to reduce the deformation of the rotor/stator with the objective of ensuring a constant air gap between the stator and the rotor. However, the application of this approach generates very heavy structures whose e.g. manufacture and transport are very costly.
EP2106013A2 shows another approach by disclosing a deflection resistant wind turbine generator in which the stator and the rotor have selectively engageable surfaces that maintain the air gap as substantially stable and permit rotation of the rotor during engagement, said engageable surfaces engaging when the rotor deflects to a predetermined amount of deflection. Moreover, EP2106013A2 also describes that said selectively engageable surfaces may include a set of internal bearings.
EP2063114A1 shows yet another approach by disclosing a wind turbine that comprises a retaining arrangement (e.g. a main frame in form of a retaining arm) which supports a supporting element of the rotor and is connected to a supporting element of the stator, so that stability of the rotor-stator structure is increased.
Nevertheless, the approaches commented in the two previous paragraphs usually involve complex geometries, introduce additional components, etc. The resulting wind turbine generators may thus be expensive and difficult to maintain.